Passengers face unprecedented delays and cancellations this weekend as Railtrack carries out the biggest programme of track renewal for a century.

Passengers face unprecedented delays and cancellations this weekend as Railtrack carries out the biggest programme of track renewal for a century.

More than 40,000 metres of track will be laid at 160 sites. Travellers who have spent a week suffering delays of up to two hours will have their patience tested as never before. Up to 300 sites could be affected by speed restrictions imposed after the Hatfield crash as 20,000 staff work until checks are complete. More than 1,800 rails have been found to have the same hairline cracks that caused the Hatfield crash.

Yesterday Tony Blair summoned Gerald Corbett, Railtrack's chief executive, to Downing Street. While conceding the industry was doing the best it could in difficult circumstances, Mr Blair also stressed the need for the work to be done as quickly as possible without causing the network to seize up.

At a separate meeting with rail executives John Prescott, Deputy Prime Minister said passengers' patience was being "stretched to the limit".

Yesterday Railtrack announced that at least one line, from Wimbledon into Clapham Junction, would be closed tomorrow for repairs. This will have a knock-one effect at Waterloo. Work is also planned for track between Liverpool Street and Ilford, Essex.

Last night at Waterloo the announcements apologising for delays and cancellations were unending. There were reports of fights among passengers as they struggled to board trains.

Jackie Griffiths, a PA trying to get home to Swanley, Kent, from London Bridge, said: "Anyone would think we've got a Third World country. In the 45 minutes I've been waiting for a train I've seen at least three separate fights - and one of those was between two women. They were hitting each other to get on the train." Staff confirmed they had to intervene in three fights.

Paul Baker, another commuter, said: "They're trying to herd us on to trains like cattle, which is making everyone get really annoyed ... I'm sure this is more dangerous than travelling at the normal speed limit."

While some operators are trying to run a full service subject to delays, First Great Western, which runs services into Paddington, said it was introducing a revised timetable from next week, meaning although there will be fewer trains they will at least run to schedule.

A spokesman for the Association of Train Operating Companies (Atoc) pleaded with travellers to be patient and to try to gather information about their journey before setting off. "It has been a nightmare for commuters but there is a level of tolerance out there at the moment. That will start to wear off if things don't start to improve." He added that the train-inquiry phone service received 500,000 calls on Thursday, more than double the usual number.

The Atoc spokesman added: "We are doing the best we can to give people accurate information but the situation is changing all the time. At one point in the West Midlands there were 10 speed restrictions; an hour later that had increased to 46 and fell back to 30 shortly afterwards ... Everyone is working flat out to try and identify the problems areas and repair the track as quickly as possible."

Rail-users groups said passengers were resigned to the disruption, although their tolerance was expected to wear off if the situation did not improve by the middle of next week.

At his Downing Street meeting yesterday Mr Corbett told Mr Blair all necessary safety inspections would be done by the middle of next week. Railtrack would then have a clearer idea of which lines would be closed or subject to speed restrictions and for how long.

After the meeting Mr Corbett said: "We have got to bash on and get it sorted. This is the biggest programme of track inspection ever seen. The network will be getting back to stability over the weekend and by the end of Tuesday we will know where we are with speed restrictions." But he admitted the situation was likely to get worse before it got better. Railtrack said the wreckage would be removed from the line at Hatfield early next week.

This weekend a hi-tech machine, currently being used to modernise the west coast line, will be brought in to lay track around remains of the buffet car. It is capable of laying 15 sleepers a minute, four times faster than conventional track- laying, by picking up old sleepers at the front and replacing them at the back.